This invention relates to heating of aircraft cabins. More specifically, this invention relates to the use of engine bleed or compressor air to accomplish the heating.
Various devices have been used in the past for heating the cabins of aircraft. Among the more effective of these devices is the combustion heater. However, combustion heaters consume fuel from the aircraft's main engine fuel system, and present problems such as greater weight and complexity, increased fire hazard, and carbon monoxide poisoning.
The advent of gas turbine power plants with attendant large quantities of hot pressurized air has reduced the need for combustion heaters. A portion of the hot pressurized air, commonly referred to as bleed air, is used for direct heating of the cabin air. Such systems include, for example, direct infusion of the bleed air into the cabin space. However, these prior art systems are limited by an insufficiency of bleed air during certain phases of engine operation, or engine power penalties associated with use of bleed air for non-engine purposes. This requires the use of supplemental cabin heating means, such as a combustion heater or the like.
The present invention contemplates the more efficient use of the available quantity of bleed air for heating the cabin space of an aircraft. The bleed air is used to heat cabin air in a heat exchanger, and then to operate a heating device for additional heating of the cabin air. This results in the cabin being maintained at a comfortably warm temperature during phases of engine operation wherein the quantity of hot bleed air from the engine is at a minimum.